fix(HTTPError): Remove dependency on blank title to determine serialization

This patch attempts to make the code easier to understand and maintain
going forward by removing the dependency between the title attribute and
the "serializable" property. The "serializable" property was renamed to
be more indicitive of the context in which it is actually used.

Closes #265
This is unrelated to the patch, but how does this work?  The caller providing anything at all in kwargs results in an error getting serialized?  Why is that?